Plastic polymers and synthetic resins have been used in various fields such as vehicles, building materials, aircrafts, railroads, home appliances, and the like. Further, various functional additives are being rapidly developed, which has increased the variety of applications for polymers. However, many polymers can burn easily and do not have fire resistance. Therefore, many polymers may be easily combusted by an exterior igniting source and may cause the fire to spread. Accordingly countries such as the United States, Japan and many European countries have passed laws requiring polymer resins to satisfy flame resistance standards to guarantee stability in the presence of a fire.
Various techniques can impart flame retardancy to polymers. Examples include synthesizing a thermally stable resin through molecule structure design, chemically improving a conventional polymer (reaction type), physically modifying a polymer by blending or compounding the polymer with a flame retardant agent (additive type) and coating or painting a polymer product with a flame retardant agent.
For example, many conventionally used and well known flame retardant methods add a flame retardant agent to a polymer resin. These additive type flame retardant agents can be classified according to their components and include halogen-containing, phosphorus-containing, nitrogen-containing, silicon-containing, and inorganic-containing flame retardant agents.
Halogen-containing flame retardant agents restrain chain reactions through a reaction with radicals that are generated in the gas during the combustion of polymers within a resin. Examples of halogen-containing compounds used to impart flame retardancy include polybromodiphenyl ether, tetrabromobisphenol-A, epoxy compounds substituted with bromine, chlorinated polyethylene and the like. Bromine-containing flame retardant agents are widely used as halogen-containing flame retardants in electronic applications because they can provide advantageous physical properties, price and flame retardancy. In addition, antimony trioxide or antimony pentaoxide are commonly used as additives in combination with halogen-containing flame retardant agents.
Bromine-containing flame retardant agents, however, may be harmful to humans and the environment. Due to the above, the Restriction of Hazardous Substances Directive (RoHS) was ratified in July 2006. Accordingly, a universally used bromine-containing flame retardant agent as known as DECA is partially being suspended from use, and the amount of the agent used is significantly decreasing.
Thus, with the concerns about the environmental impact of halogen-containing flame retardant agents, there is an increasing trend to use phosphorous flame retardant agents. Classes of phosphorous flame retardant agents include phosphates, phosphine oxides, phosphonates, and the like. Phosphorous flame retardant agents can have excellent flame retardancy in a solid phase reaction, particularly for plastics with a high oxygen content. Further, phosphorous flame retardant agents can attain flame retardancy in combination with a char forming material such as polycarbonate resin or polyphenylene ether resin. Examples of typical flame retardant phosphorous compounds include aromatic phosphorous esters such as triphenylphosphate, resorcinol bisphenol phosphate, and the like.
U.S. Pat. No. 4,692,488 discloses a thermoplastic resin composition comprising non-halogen aromatic polycarbonate resin, non-halogen styrene-acrylonitrile copolymer, non-halogen phosphorous compound, tetrafluoroethylene copolymer and small amount of ABS copolymer. U.S. Pat. No. 5,061,745 discloses a flame retardant resin composition comprising aromatic polycarbonate resin, ABS graft copolymer, styrenic copolymer, phosphorous ester and tetrafluoroethylene copolymer. However, large amounts of phosphorous ester must be added in order to achieve flame retardancy.